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The twin‐arginine translocation (Tat) system is essential for Rhizobium –legume symbiosis
Author(s) -
Meloni Stefania,
Rey Luis,
Sidler Stephan,
Imperial Juan,
RuizArgüeso Tomás,
Palacios José M.
Publication year - 2003
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03510.x
Subject(s) - biology , mutant , rhizobium leguminosarum , sinorhizobium meliloti , signal peptide , biochemistry , arginine , symbiosis , rhizobium , microbiology and biotechnology , rhizobiaceae , bacteria , gene , peptide sequence , genetics , amino acid
Summary The Tat (twin‐arginine translocation) system mediates export of periplasmic proteins in folded conformation. Proteins transported via Tat contain a characteristic twin‐arginine motif in their signal peptide. Genetic determinants ( tatABC genes) of the Tat system from Rhizobium leguminosarum bv. viciae were cloned and characterized, and a tatBC deletion mutant was constructed. The mutant lacked the ability for membrane targeting of hydrogenase, a known Tat substrate, and was impaired in hydrogenase activity. Interestingly, in the absence of a functional Tat system, only small, white nodules unable to fix nitrogen were induced in symbiosis with pea plants. Analysis of nodule structure and location of green fluorescent protein (GFP)‐tagged bacteria within nodules indicated that the symbiotic process was blocked in the tat mutant at a stage previous to bacteria release into cortical cells. The R. leguminosarum Tat‐deficient mutant lacked a functional cytochrome bc 1 complex. This was consistent with the fact that R. leguminosarum Rieske protein, a key component of the symbiosis‐essential cytochrome bc 1 complex, contained a typical twin‐arginine signal peptide. However, comparative analyses of nodule structure indicated that nodule development in the tat mutant was arrested at an earlier step than in a cytochrome bc 1 mutant. These data indicate that the Tat pathway is also critical for proteins relevant to the initial stages of the symbiotic process.

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